Thiết bị & Hệ thốngCâu 266 / 521
Why must a motor circuit have both overload protection AND short-circuit/ground-fault protection?
a.They are the same device required in two locations
b.Overload devices protect against sustained overcurrents from motor running conditions, while short-circuit/ground-fault devices clear high-magnitude faults
c.Overloads clear faults faster than breakers
d.Short-circuit devices also sense motor running overload
Giải thích
Overload devices (sized ~115-125% of FLA) protect the motor and conductors from sustained overloads but are too slow for faults; branch-circuit short-circuit/ground-fault devices (sized much higher per Table 430.52) clear high fault currents. NEC 430 requires both because each addresses a different hazard.
Trích dẫn luật: 2023 NEC §430.31Luyện miễn phí toàn bộ 521 câu hỏi — không cần đăng ký.
Câu hỏi liên quan cùng chủ đề
- NEC 450.3(B) overcurrent protection percentages for transformers 1000 V or less are based on what?
- What is the rated primary current of a 25 kVA, single-phase transformer with a 240 V primary?
- A 45 kVA, three-phase transformer has a 208 V secondary. What is the rated secondary current?
- A 30 HP, 460 V, three-phase motor has an FLC of 40 A. What is the minimum ampere rating of the motor disconnecting means (115% of FLC)?
- Under NEC 430.102(B), where must the disconnecting means for a motor generally be located?
- Per NEC Table 430.248, what is the full-load current of a 3 HP, single-phase, 115 V motor?
Cập nhật gần nhất: · quy trình kiểm tra
Đội Ngũ Biên Tập PrepPass · Đối chiếu với California CSLB C-10 Electrical Trade Examination · Quy trình kiểm tra